1. Field of the invention
The present invention relates to a trimmer device and a trimming method, and more particularly, to a trimmer device and a trimming method using switches to control an equivalent impedance value.
2. Description of the Related Art
Due to variances in fabrication, circuit characteristics such as resistance or capacitances may shift away from ideal values during the manufacture of integrated circuits. The above-mentioned variances in circuit characteristics may reduce the operation efficiency of circuits. In other cases, these variances may even cause malfunction during the circuits' operation.
However, during chip packaging, it is nearly impossible to adjust every chip device if time and cost are issues of concern. Please note that, for the perspective of an analog circuit, a primary goal is to maintain the value of reference signals residing in the integrated circuit (IC) in order that the values are equalized to the ideal values of the original circuit design. (For example, this is to maintain the voltage levels of specific nodes.) Therefore, a mechanism for performing the aforementioned adjusting operation is necessary for those skilled in the field of the art.
Please refer to FIG. 1. FIG. 1 is a diagram of a conventional trimmer device 100. As shown in FIG. 1, the trimmer device 100 is utilized to adjust the reference voltage VF of the target circuit 110. The trimmer device 100 comprises three serial-connected resistors 120, 130, and 140 and three fuses 150, 160, and 170. As shown in FIG. 1, the conducting conditions of the fuses 150, 160, and 170 determine the equivalent impedance value of the resistors 120, 130, and 140. In other words, if the fuses 150, 160, and 170 are not melted, each of the fuses 150, 160, and 170 will act as a short circuit. During this time, corresponding resistances of the resistors 120, 130, and 140 are ignored.
On the other hand, if one of the fuses 150, 160, and 170 is melted, one corresponding resistor among the resistors 120, 130, and 140 will be conductive (i.e., the electric current can pass through the corresponding resistor), and a voltage can be generated across the corresponding resistor. Therefore, the voltage level of the reference voltage VF can still be further adjusted.
Furthermore, please refer to FIG. 2. FIG. 2 is a diagram of another conventional trimmer device 200. The trimmer device 200 is similar to the trimmer device 100. The difference between them is that the resistors 220, 230, and 240 and the fuses 250, 260, and 270 are connected in series respectively. The operation and function of the trimmer device 200 is similar to that of the trimmer device 100. The trimmer device 200 also manipulates the equivalent impedance of the resistors 220, 230, and 240 by using the conducting condition such that the voltage level of the reference voltage VF can be adjusted.
Through the above-mentioned mechanism, during chip packaging, the manufacturer can utilize an external testing device (not shown) to detect the reference voltage. Additionally, the testing device can detect other reference signals. For example, the testing device can input a testing voltage and then detect a testing current corresponding to the testing voltage. The testing device can select some of the fuses 150, 160, and 170, which are to be melted, according to the variance of the reference voltage. In this way, the equivalent impedance provided by the resistors 120, 130, and 140 can be adjusted such that the reference voltage is also adjusted to the ideal value of the original circuit design.
Unfortunately, the above-mentioned trimmer devices 100 and 200 have some disadvantages. First, sometimes the fuses are not melted completely. So these fuses, which are not melted completely, have resistances. In this way, the resistance provided by the partially melted fuses may correspondingly influence the voltage level of the reference voltage VF. This situation prevents the original trimmer device from operating correctly. In addition, in the above-mentioned trimming mechanism, the equivalent impedance provided by the resistors can only be adjusted upward. Therefore, if the resistance of the target circuit is larger than the ideal value, the above-mentioned trimmer device is not capable of improving the situation. At this time, in order to raise the yield of the chip, the resistance of the target circuit has to be assigned a lower value when the chip is designed, where the lower value is lower than the ideal value. In this way, during chip packaging, the trimmer device is utilized to adjust the resistance upward to the ideal value. However, the above-mentioned trimming mechanism makes the adjustment of all chips necessary. Therefore, although the yield can be increased, a lot of time and costs are required using this method.